Certain hydraulic systems include a tank or reservoir that receives and stores hydraulic fluid. These hydraulic systems often create pressures and vacuums within the tank or reservoir during use. Breather vents are typically provided in the tank to ensure that uncontaminated air is provided into the system and that the proper pressures are maintained for efficient and safe operation of the system.
For various reasons, water may find its way into the hydraulic fluid. For example, rain may leak into externally located reservoirs or seep through reservoir covers, access panels, breathers or worn seals. Additionally, condensation from air in reservoirs and other system areas can be a source for water contamination. Water can also enter the fluid system from the process side, from leaky heat exchangers or coolers, or direct ingression of process water, such as cooling water, washdown water or steam.
Water in hydraulic fluid is undesirable for a number of reasons. For example, water contamination can deplete some additives and react with others to form corrosive by-products which attack some metals. In addition, water contamination can reduce lubricant film-strength, which leaves critical surfaces vulnerable to wear and corrosion, as well as reduce filterability, increase air entrainment ability and increase the likelihood of cavitation.
Various methods exist for removing water from hydraulic fluid. One such method is vacuum dehydration, which uses purifiers to dry hydraulic fluids and lubricants by exposing them to a partial vacuum. Exemplary vacuum dehydration methods include flash distillation vacuum dehydration and mass transfer vacuum dehydration. While both processes utilize the concentration gradient between the fluid and the evacuated air to evaporate the water from the fluid, the flash distillation technology also applies heat to further boil off more water and operates at a higher vacuum. This makes flash distillation more rapid, as it removes more water from the fluid than a mass transfer device.
Conventionally, vacuum dehydration systems utilize a moisture sensor to determine a moisture level in the fluid and thus to determine when dehydration is complete. A problem with using moisture sensors, however, is that they tend to have slow response times (particularly when the fluid is above saturation), which can lead to less than optimal control of the dehydration process.